android 多点触摸绘画demo

public class GestureView extends View {    public GestureView(Context context) {        super(context);    }    TwofingerGestureDetector detector;    Paint paint;    public GestureView(Context context, AttributeSet attrs) {        super(context, attrs);        detector = new TwofingerGestureDetector();        paint = new Paint();        paint.setStyle(Paint.Style.STROKE);        paint.setStrokeWidth(30);    }    SparseArray mActivePointers = new SparseArray<>();    @Override    public boolean onTouchEvent(MotionEvent event) {        //当前DOWN或者UP的是手指的index        int curPointerIndex = event.getActionIndex();        //通过index获得当前手指的id        int curPointerId = event.getPointerId(curPointerIndex);        int actionMasked = event.getActionMasked();        switch (actionMasked) {            case MotionEvent.ACTION_DOWN:            case MotionEvent.ACTION_POINTER_DOWN:                PointF pointF = new PointF();                pointF.x = event.getX(curPointerIndex);                pointF.y = event.getY(curPointerIndex);                Path p = new Path();                p.moveTo(pointF.x, pointF.y);                mActivePointers.append(curPointerId, p);                break;            case MotionEvent.ACTION_MOVE:                for (int size = event.getPointerCount(), i = 0; i < size; i++) {                    Path path = mActivePointers.get(event.getPointerId(i));                    if (path != null) {                        path.lineTo(event.getX(i), event.getY(i));                    }                }                break;            case MotionEvent.ACTION_UP:            case MotionEvent.ACTION_POINTER_UP:                mActivePointers.remove(curPointerId);                break;        }        invalidate();        return true;    }    @Override    protected void onDraw(Canvas canvas) {        canvas.drawColor(Color.WHITE);        for (int size = mActivePointers.size(), i = 0; i < size; i++) {            Path path = mActivePointers.valueAt(i);            canvas.drawPath(path, paint);        }    }}
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